Titanium anodizing

For decorative purposes, the anodizing of chemically pure titanium metal parts made of ASTM grades 2 and 4 can be conducted as follows. 

Degreasing. The removal of grease and organic coatings of titanium parts consists in soaking them in a tank of hot chlorinated solvent (e.g., dichloromethane, trichloroethylene) 

Chemical etching. Cleaned parts are immersed for 10 to 30 s into a fluoronitric mixture (25 to 35 wt.% HNO3 with 15 to 30 cm HF per liter) followed by a thorough rinse with deionized water. 

Gambogi, J. (1993) Annual Report Titanium-1992. V.S. Bureau of Mines, Washington, D.C., p. 1. 

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Titanium has potential use in desalination plants for converting sea water into fresh water. The metal has excellent resistance to sea water and is used for propeller shafts, rigging, and other parts of ships exposed to salt water. A titanium anode coated with platinum has been used to provide cathodic protection from corrosion by salt water. 

The electrolysis is conducted at 90—95°C and an anode current density of about 50 120 A/m when using lead alloy anodes and lead cathodes. Using graphite electrodes, the current density is from 70 100 A/m using titanium anodes and graphite cathodes, the current density is 50 80 A/m (82). 

Cathodic Protection Systems. Metal anodes using either platinum [7440-06 ] metal or precious metal oxide coatings on titanium, niobium [7440-03-17, or tantalum [7440-25-7] substrates are extensively used for impressed current cathodic protection systems. A prime appHcation is the use of platinum-coated titanium anodes for protection of the hulls of marine vessels. The controUed feature of these systems has created an attractive alternative... 

P. S. S. Hayfteld and W. R. Jacob, "Platinum—Iridium-Coated Titanium Anodes ia Brine Electrolysis," paper presented 2i. A.dvances in Chlor-A.lkali Technology, London, 1979. 

Sodium nitrite has been synthesized by a number of chemical reactions involving the reduction of sodium nitrate [7631-99-4] NaNO. These include exposure to heat, light, and ionizing radiation (2), addition of lead metal to fused sodium nitrate at 400—450°C (2), reaction of the nitrate in the presence of sodium ferrate and nitric oxide at - 400° C (2), contacting molten sodium nitrate with hydrogen (7), and electrolytic reduction of sodium nitrate in a cell having a cation-exchange membrane, rhodium-plated titanium anode, and lead cathode (8). 

Krebs steel steel, with titanium anode cover plate titanium inlet and oudet reducer connections titanium... 

Since the 1960s titanium mesh anode baskets have been used (21), especially in nickel plating solutions. Nickel anodes in the form of small round buttons and pellets combined with the titanium anode basket allows a constant anode area to be maintained with a minimum of effort. 

A current with ripples can lead to a high consumption rate for platinized titanium anodes and their premature failure. The residual ripple should be limited to 5% (see Section 7.2.2) [7],... 

Plate anodes were used for corrosion protection in order to avoid damage due to erosion and cavitation. These consisted of enamelled steel bodies in which a metal oxide-coated titanium anode 1 dm in surface area was fitted. The enamel... 

In the field of electrowinning and electrorefining of metals, titanium has an advantage as a cathode, upon which copper particularly can be deposited with finely balanced adhesion that allows the electrodeposited metal to strip easily when required. Titanium anodes are also being employed as a replacement for lead or graphite in the production of electrolytic manganese dioxide. 

In aqueous chloride where it is necessary to use platinised titanium anodes coated over only part of their surface, e.g. titanium rod tipped with a thin platinum film, it may be necessary to limit the applied voltage to 12 V. 

The anodic behaviour of platinum and certain of its alloys is of considerable technical importance, since they can be employed under a wide range of conditions without appreciable corrosion, and often in circumstances where no other metal can be used. Their use industrially has recently been extended by applying them as thin coatings to a substrate of a passive metal such as tantalum or, more commonly nowadays, titanium, to reduce the cost. Platinised titanium anodes are discussed in detail in Section 11.3. 

Cotton was the first to publish results on platinised titanium as an anode material, and the first commercial installation utilising platinised titanium anodes was completed in 1958 at Thameshaven for the protection of a Thames-side jetty. 

The Operational Characterisics of Platinised-Titanium Anodes Platinised-titanium anodes have the disadvantage that the protective passive him formed when titanium is made anodic in certain solutions can breakdown. This could result in rapid pitting of the titanium substrate, leading ultimately to anode failure. The potential at which breakdown of titanium occurs is dependent upon the solution composition, as is evident from Table 10.16. 

Platinised titanium anodes may be operated at current densities as high as 5 400 Am however at these current densities there is the possibility that the breakdown potential of titanium may be exceeded. The normal operating current density range in seawater is 250-750 Amwhilst that in brackish waters is given as 100-300 Am with values within the range... 

The effect of temperature on the consumption rate of platinised titanium anodes has not been found to be significant over the ranges normally encountered in cathodic protection installations, although at elevated temperatures of 90-95°C, consumption rates of 570mg A y in 0-02<7o Na2S04 and 12<7o NaCl solutions have been reported. ... 

Early failures of platinised titanium anodes have been found to occur for reasons other than increased consumption of platinum or attack on the titanium substrate caused by voltages incompatible with a particular electrolyte. The following are examples ... 

The superimposition of a.c. ripple on the d.c. output from a transformer rectifier can under certain circumstances lead to increased platinum consumption rates and has been the subject of considerable researchIndeed, when platinised titanium anodes were first used it was recommended that the a.c. component was limited to 5% of the d.c. voltage . 

Platinised-titanium anodes may also be used in soils when surrounded by a carbonaceous backfill. Warne and Berkeley " have investigated the performance of platinised-titanium anodes in carbonaceous backfills and conclude that the anodes may be successfully operated in this environment at a current density of up to 200 AmThis also supplements the findings of Lewis, who states that platinised-titanium anodes may be used in carbonaceous backfill without breakdown of the titanium oxide film. Success with platinised-titanium anodes has been reported with anodes operating at a few tens of Am and failures of anodes have often been attributed to operation at high current densities . 

The oxide coatings are porous and therefore the limitations on operating voltage for platinised titanium anodes apply as well to the oxide-coated titanium electrodes. It has been reported that breakdown of mixed metal oxide anodes may occur at 50-60 V in low-chloride concentration water but at only 10 V in chloride-rich environments . 

Platinised titanium These anodes are usually in the form of titanium rod, tube or wire with a coating of platinum 2-5 to 5-0 tm thick. Diameters are generally in the range 3 to 25 mm. In order to reduce the voltage drop in very long anodes, a copper cored variety is available. Platinised titanium anodes may also be used in mesh or plain sheet form and can be fabricated to suit particular applications. 

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